Radio signaling system



July' 23, 1929.

V. M. GRAHAM RADIO SIGNALING SYSTEM Filed Sept. 1G, 1925 n' PILOT LAMP im 'i E* w e I i l :1 I i Il I FIG.4

INVENTOR v VIRGn. M. GRAHAM ATTORN EY BYQWM.

eectscn ,the .vonagaampliie Patented July 23, '1929.

PATENT-onion g VIRGIL M. GRAHAM, oF ROCHESTER, k.new YORK, ASSreNoRmo THE smRoMBRRecARLsoNTELnP-HONE MANUFACTURING COMRANY, or RooHEsTnR, Nnw YoRK, e

CORPORATION A0F NEW YORK.

RADIO SIGNALING SYSTEM.

Application .filed Septemberv 16, .1925. Serial No. 56,740.

This invention relates to amplifiers and more particularly to multi-stage ampli-fiers cemploying an electron discharge tube ineach stage.

'In multi-stage amplifiers vhaving electron tubes, especiallythose employed foramplifying radio-frequency currents, itl is .customary to couple the output circuit of one electron tube to the input circuit of a second electron tube, by means ofanair-core transformer. It has been recognized in lsuch radio-frequency amplifiers especially those in which each of the stages are tuned to the frequency of the incoming signal, that it is desirable to have a 4high degree of voltage amplification, resulting from the design of the transformer. In the'past, such multi-stage radio-frequency amplifiers have `notamplified all portions of the frequency range to an' equal amount, `in

other,` words these amplifiers are less efficient at certain portions .of the frequencyv range, than at others. In one type of radio-fre- .quency amplifiers, whichv has proven especially satisfactory, it is customary to provide a neutralizing winding in `addition to the primary and secondary windings of the transformers, which when incorporated with a neutralizing condenser in the circuits of a stage, serves to prevent regeneration by ehminating capacity coupling between the ,input and output circuitsof such a stage.

The present invention resides in the method of coupling two or more stages of a multistage vradio-frequency amplifier, wherein the voltage amplification is rendered more nearly uniform throughout a `determined frequencyv variation to introduce loss in the tuned input circuit.

The inventionfurther consists in controlling the frequencycharacteristics of-a -radiofrequency transformer .by introducing a dielectric loss intothetuned input circuit with which vit associated. Y

Referring to the drawings, Fig. 1 ,repre- ,sent-sa multi-stage tuned radio-frequency rek@aimingset. Fie, 2,115@ ,Chart timing the nat various ,wavelengths of varying the spacing between Vlthe primary and neutralizing windings of a transformer.. Fig, f3 is a chart having var lous graphs showing the volt-age` amplification plotted as afunction of turns lper inch of the primary and neutralizing coils atseveral different wave lengths. Fig. .4 is a porspaced grooves, in .whichthe primary and neutralizing windings are wound. Fig. 6 shows av modified form of the invention.'

Yieferring tothe drawings, Fig. 1 reprei .sents three units of tuned"radio-frequency amplification, in which the units arefdesignated 5,6 and 7 respectively. The amplified signal energy of these,radio-frequency units is rectified yin a detector V8 .andthe rectified Ysignals Vmay be amplified and ,translated into soundby a loud speaker unit 9.

This receiver' is provided with .an antenna .29, which includes the primary winding 10 of la vradio-freopiency transformer of' the aircore type, having a secondary winding ,11. A yariablecondenser ,12 isconnected across the terminals of ,this transformer toprovide a .tuned input circuit for the electron discharge rtube V1. An intermediate point on the secondary winding 11 is connected to the grid 13y of this tube, while the lower yterminal of ,this winding is connected to one side ofthe heating `systemof the filament 33 of this same tube. The output circuit of this .tube ,is connected from its plate 14'throughtheprimary winding 15 o fa radio-frequency transformer "171, thence through the conductor 16, the B .battery 17, pilot lamp 18', and theconductor 1 9 to the heating circuit ofthe filament 13. As is V well known there is an undesirable coupling between the input circuit'and the out- -put circuit or plate circuit of an electron discharge tube,d.u e to the inherent capacity exlsting between its elements ,such as the grid 13and plate 14,. rEhis capacity coupling .may be Aeliminated v by providing a net itralizing Condenser' 18 and a neutralizing winding 19', .so arranged as to apply a capacity current to lthe grid 13, equal and oppositeto that which Hwould normally be applied to the grid through .the mentioned vinherent capacity. The secondary winding 2O ofthe transformer "is included inthe linput circuit of a .ascend fie electron discharge device V2 also provided with a neutralizing condenser and neutralizing winding as in the case of the rstV men- 'tioned device. This device is coupled tothe third stage of radio-frequency amplification, by means of a transfori'ner T2, similar in structure and arrangement to that shown at T1.v The third unit of radio-frequency ampliiier, including the well known electron discharge tube V3, coupled to the detector tube D, by means ofa `radio-frequency transformer T3, .similar to the transformers T1 and T2. The output circuitof the detector D coupled to an ampliticrand loud speaker system, (designated 9, .which may beof any well known lstruct-ure and arrangement.

vplurality of these. stages arranged in cascade constitute a multi-stage amplifier. n

Each of the transformers T1, T2 and T3 consists of a primary winding and a neutralizing winding 19 which are parallel wound on a tube of insulating material 21,

and a secondary winding 2O wound on a sec-- ond tube 33 of insulating material arranged tov closely encircle the first tube. As indicated in Fig. 5, the tube 21 has grooves spaced a strictly accurate predetermined distance apart, in which grooves'the primary and neutralizing windings are wound. e noted that these turns are alternately positioned on the insulating tube and may be applied by winding the wires of the two coils simultaneously.

The frequency characteristic ofi'adio-frequency transformers such as are used in a tuned radioefrequency amplifier may be regulated in part by varying the loss inthe tuned input circuit of each of the stages. It has been discovered that this loss is most effective when present as a .dielectric loss and it V`inay be obtained by reflecting into the circuit of the secondary winding of the transformer,

Vthe dielectric loss between the alternately wound turns of the primary and the neutralizing winding of the transformer, ]ust referred to.

` In order to indicate the effect of varying the spacing between the several turns of the vprimary' and neutralizing windings, reference is made to Fig. 2, wherein the graphs A,

the number of turns per inch.V In deriving these graphs, theprimary windings of the It will be transformers consist'of 211 turns of #29 doulwinding each wound with 2O turns per inch,

and the transformer represented by graph B had these windings wound with 16 turns per inch, l while the transformer represented by graph C was wound with 12 turns per inch in each of these windings.

Fig. 3 shows graphs indicating the variation of the vvoltage ampliiication of a timed radio-frequency transformer at resonance with respectito the spacing of the number of primary turns per inch with the saine number of primary, neutralizing and seeondarylturns, that is, with a primary winding consisting of 24 turns of #29 double silk covered wire on tubing of two and one-half inches in diameter and a neutralizing winding consisting of 25 turns of #29 double silk covered wire, parallel wound with the primary winding on the same tubing, while the secondary winding consists of 63 turns of :#:20 enamelled wire on tubing of two and three-fourths incheson its outer diameter, having 23 turns per inch. In this figure, curve AEv represents awave length of 250vmeters, curve F a wave length of 3501metcrs, curve G a wave length of Vmeters and curve H a wave length of 550 meters.

In Fig. 6 there is illustrated a modified forni of the, invention, in which a single amplifier stage with other associated circuits shows `the relation of the invention to a multi-stage amplifier.

In a radio receiver of the typein which timed circuits, and means for balancing against undesirable couplings otherthan the neutrodyne arrangement of Figtrl are employed, it is desirable to control th eamplifica- 'etionso that more uniform amplification is obtained over the whole frequency range, and

so that `the an'ipliiication can. be reduced at the higher frequencies to render the receivers stable against oscillations. Y V Y.

In the case ofthe receiver' vof Fig. 1, the capacity between the neutralizing Winding, such' as 19 Yand the primary winding, such as 15 furnishes a dielectric loss, which serves to straighten out the frequency characteristics of the amplifier. In yother types of `radifrequency amplifiers, such asl shown invFiOf. 6, where a neutralizing winding such as previously described is not used, the frequency characteristic curve will be lvery' steep, slope ing upward at the higher frequencies. In

llO

cause the voltage is not of sufficient amplitude n and because the effectiveness of the dielectric loss varies as the square of the applied voltage.

lith a` view of increasing the voltage that i it is possible to apply in addition to the distributed capacity ofthe primary winding, it is necessary to take advantage of the transformer action. Thus in addition to the primary win ding in the output circuit of the vacuum tube V, an auxiliary coil 5l is provided, which is wound parallel to the primary winding with a one to one ratio of turns. The lower end ofthe coil 51 is left unconnected, while the other end is attached to the terminal of the primary winding, which is connected to the positive pole of the B battery. It will be noted that in this arrangement the point of the highest self-induced potential of the primary coil 50, that is the upper terminal, is opposite the low po'- tential or upper terminal of the coil 5l and that the terminal of the primary coil having low self-induced potential is opposite to the terminal of the coil 51, which is of high induced potential. F rom this, it will be seen that the potential differences between the two windings throughout their whole length is practically equal to the self-induced potential across the primary coil.. This arrangement provides a much greater dielectric loss than is otherwise possible, owing to the large amount of capacity between the` two windings and further due to the high potential applied.

This dielectric loss may be reficcted into the secondary coil 52 of the transformer to provide uniform amplification over a wide predetermined range of frequencies.

That I claim is:

1. In a multi-stage tuned radio-frequency amplifier', having an electron discharge device in each stage provided with an input circuit and an output circuit, a transformer with a primary winding and a secondary winding for coupling the output circuit of one stage to the input circuit of a second stage, and means for neutralizing capacity coupling between the input circuit and the output circuit of each stage including a neutralizing winding, the method of producing amplification over a .wide range-'of frequencies, which consists in employing such spacing between the turns of the primary and neutralizing windings as to introduce predetermined loss into the input circuit which loss varies with the frequency.

2. In an amplifier, two electron discharge tubes, each having filament, grid and platey electrodes, with inherent capacity existing there-between, an input circuit connected 'between the grid and filament of eachy electron discharge tube, an output circuit including a plate and filament, a transformer having a primary winding in the output circuit of the first electron discharge tube and a secondary winding in the input circuit of said second electron discharge .tube'to couple said last mentioned circuits together, a neutralizing winding and a neutralizing capacity connected between the grid and filament of said first electron discharge tube, and a commen tubular support on which said primary and neutralizing windings are alternatcly wound with uniform predetermined spacing between their turns to introduce a predetermined loss into the input circuit of .aid second electron discharge tube, which loss varies with the signal frequency.

8. in an amplifier, two electron discharge tubes each having filament, grid rand plate electrodes with inherentcapacity exist-ing there-between, an input circuit connected between the grid and filament of each electron discharge tube, an output circuit includingv each plate and lament, a transformer having a primary winding in the output circuit of the first electron discharge tube and a secondary winding in the input circuit of said second electron discharge tube to couple said last mentioned circuits together, a neutralizing winding and a neutralizing capacity connected in circuit between the grid and filament ofsaid first electron discharge tube, and a common tubular support with grooves spaced a predetermined distance apart, said primary and neutralizing windings being alternately wound in the grooves of said support to introduce a 'predetermined loss into the input circuit of said second electron discharge tube, which loss varies with the signal frequency.

In Witness whereof, I hereunto subscribe my name this 10th day of September, A. D. 1925.

VIRGL M. GRAHAM. 

